A conventional apparatus of the type described is shown in FIG. 7.
The apparatus shown includes a hydraulic pump 1 having a discharge or delivery passage la to which a first and a second operating valve 1 and 3 are connected in parallel with each other. The first operating valve 2 has a first fluid operated actuator 4 connected thereto via a pressure compensating valve 6. Likewise, the second operating valve 3 has a second fluid operated actuator 5 connected thereto via a pressure compensating valve 6'. A shuttle valve 7 is also connected as shown for selectively sensing the one of the respective load pressures (maximum load pressure) in the actuators 4 and 5 that is higher than the other. The maximum load pressure sensed by the shuttle valve is imported into the pressure compensating valves 6 and 6'.
The pressure compensating valves 6 and 6' have a set pressure determined by a maximum load pressure that develops in the actuators 4 and 5. The pressure compensating valves 6 and 6' on the set pressure determined operates to maintain constant the difference in pressure across the inlet and outlet sides of each of the first and second operating valves 2 and 3. This permits the first and second actuators 4 and 5 to be fed with pressure fluid in respective volumetric flows proportioned in accordance with the amounts of operation for (thus the openings in) the first and second operating valves 2 and 3.
In the prior pressure fluid supply and delivery apparatus described above, if, for example, the second actuator 5 is lower in load while the first actuator 4 is higher in load, the pressure compensating valve 6' on the low load side becomes smaller in the area of opening than the pressure compensating valve 6 on the higher load side. As a consequence, with a given pressure of fluid discharged from the hydraulic pump 1 prevailing up to both the pressure compensating valves 6 and 6', a large loss (loss in pressure) develops in the fluid of an elevated pressure that passes through the pressure compensating valve 6' on the lower load side.